Asteroids: How safe are we?

Many people were worried the world was going to end over the weekend, due to a predicted close encounter with an asteroid.

In the end we survived, but the reality is that asteroid was one of 34,000 just in the piece of space between Mars and Jupiter, says AUT ecology professor Steve Pointing.

"In low-Earth there's an awful lot of space junk, but of course when that collides with other bits of space junk it tends to burn up before re-entry because they're small objects, but what is more of a worry is these large asteroids and certainly when they larger than about 150 metres wide, so larger than say an airbus, that's when they really cross the threshold from something to observe to something to be really worried about."

The bigger the asteroid, the larger the potential damage, says Prof Pointing.

"As you get larger and larger with these asteroids, they're travelling at 65,000km/h so they have a huge amount of stored energy," he says.

"Once they hit a solid object like Earth they need to release that energy and so something for example one-an-a-half to two-kilometres wide is going to release more energy than every nuclear weapon on the planet combined."

It is estimated that the asteroid which wiped out the dinosaurs was 10 kilometres wide.